On 16.01.24 14:47, Ard Biesheuvel wrote: > On Tue, 16 Jan 2024 at 14:44, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: >> >> On 16.01.24 09:36, Ard Biesheuvel wrote: >>> On Tue, 16 Jan 2024 at 06:21, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: >>>> >>>> On 15.01.24 18:34, Ard Biesheuvel wrote: >>>>> On Sat, 13 Jan 2024 at 11:35, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: >>>>>> >>>>>> On 12.01.24 19:56, Palmer Dabbelt wrote: >>>>>>> On Fri, 12 Jan 2024 10:51:16 PST (-0800), Ard Biesheuvel wrote: >>>>>>>> Hi Jan, >>>>>>>> >>>>>>>> On Fri, 12 Jan 2024 at 19:37, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: >>>>>>>>> >>>>>>>>> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >>>>>>>>> >>>>>>>>> The cflags for the RISC-V efistub were missing -mno-relax, thus were >>>>>>>>> under the risk that the compiler could use GP-relative addressing. That >>>>>>>>> happened for _edata with binutils-2.41 and kernel 6.1, causing the >>>>>>>>> relocation to fail due to an invalid kernel_size in handle_kernel_image. >>>>>>>>> It was not yet observed with newer versions, but that may just be luck. >>>>>>>>> >>>>>>>>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >>>>>>>>> --- >>>>>>>>> >>>>>>>>> Something like this should go to stable as well, but we will need >>>>>>>>> rebased patches. >>>>>>>>> >>>>>>>>> drivers/firmware/efi/libstub/Makefile | 2 +- >>>>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>>>>>> >>>>>>>>> diff --git a/drivers/firmware/efi/libstub/Makefile >>>>>>>>> b/drivers/firmware/efi/libstub/Makefile >>>>>>>>> index 06964a3c130f..d561d7de46a9 100644 >>>>>>>>> --- a/drivers/firmware/efi/libstub/Makefile >>>>>>>>> +++ b/drivers/firmware/efi/libstub/Makefile >>>>>>>>> @@ -28,7 +28,7 @@ cflags-$(CONFIG_ARM) += -DEFI_HAVE_STRLEN >>>>>>>>> -DEFI_HAVE_STRNLEN \ >>>>>>>>> -DEFI_HAVE_MEMCHR >>>>>>>>> -DEFI_HAVE_STRRCHR \ >>>>>>>>> -DEFI_HAVE_STRCMP -fno-builtin >>>>>>>>> -fpic \ >>>>>>>>> $(call >>>>>>>>> cc-option,-mno-single-pic-base) >>>>>>>>> -cflags-$(CONFIG_RISCV) += -fpic -DNO_ALTERNATIVE >>>>>>>>> +cflags-$(CONFIG_RISCV) += -fpic -DNO_ALTERNATIVE -mno-relax >>>>>>>> >>>>>>>> Can we detect the presence of these references (via the relocation >>>>>>>> type)? We already do something similar for ordinary absolute >>>>>>>> references too. >>>>>>> >>>>>>> If there's no `__global_pointer$` symbol then the linker won't make >>>>>>> GP-relative relaxations (because it doesn't know where GP is). We >>>>>>> usually define that symbol in the linker script, but I'm not entierly >>>>>>> sure how libstub gets its linker script... >>>>>>> >>>>>> >>>>>> The stub seems to be linked together with the rest of the kernel, thus >>>>>> the regular arch/riscv/kernel/vmlinux.lds.S is used. >>>>>> >>>>> >>>>> Indeed - the EFI stub is part of the same executable as vmlinux, we >>>>> just mangle the symbol names to ensure that only code that can be >>>>> safely called from the EFI stub can be linked to it. >>>>> >>>>> If the effect of -mno-relax is to stop emitting R_RISCV_RELAX >>>>> relocations, we should perhaps add those to the STUBCOPY_RELOC-y >>>>> Makefile variable? (in the same file). BTW R_RISCV_HI20 doesn't seem >>>>> like the right value there to begin with: the idea of that is to >>>>> disallow ELF relocations that evaluate to expressions that can only be >>>>> known at runtime (like absolute addresses for global pointer >>>>> variables) >>>> >>>> How to do that best? Simply replace R_RISCV_HI20 with R_RISCV_RELAX? >>>> >>> >>> We'll need to keep the HI20, in fact - I got confused between HI20 and >>> PCREL_HI20, and the former is actually used for 32-bit absolute >>> addresses in 32-bit code. >>> >>> This seems to do the trick: it disallows relaxation relocations and >>> native word sizes absolute references. AFAICT, those are the only ones >>> we should care about. >>> >>> STUBCOPY_RELOC-$(CONFIG_RISCV) := -E >>> R_RISCV_HI20\|R_RISCV_$(BITS)\|R_RISCV_RELAX >> >> I would suggest to do that on top of this patch. Want me to write such a >> patch, or will you? You can probably more fluently explain why >> R_RISCV_32/64 is important, I would first have to understand what that >> is exactly. :) >> > > Sure, I can take care of that. > Perfect. > For your patch, > > Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > I'll queue this up as a EFI fix. Thanks. Will you take care of stable, or should I once the commit was merged? Jan -- Siemens AG, Technology Linux Expert Center